Cam for control of combustion fuel-to-air ratio

ABSTRACT

Optimum fuel-to-air ratio over the entire operating range of a boiler fuel burner is obtained by having a motor, which is driven in response to boiler temperature or pressure changes, operate a damper and fuel valves simultaneously. A cam and follower reposition the fuel valves coordinately with a directly driven damper. Means are provided to adjust the cam contour over its length so optimum fuel-to-air ratios prevail for all positions of the damper. The follower is positively engaged with the cam.

United States Patent Turecek et al.

3,685,364 1451 Aug. 22, 1972 [54] CAM FOR CONTROL OF COMBUSTIONFUEL-TO-AIR RATIO [72] Inventors: Joseph L. Turecek, Brown Deer; GlennD. Craig, Menomonee Falls; David T. Feuling, Beaver Dam, all

' of Wis.

[73] Assignee: Aqua-Chem, Inc.

[22] Filed: July 24,1970

[21 Appl. No.: 57,985

[52] US. Cl. ..74/55, 74/568 FS, 74/569 [51] Int. Cl ..Fl6h 53/00 [58]Field of Search ..74/55, 568 FS, 569

[56] References Cited UNITED STATES PATENTS 3,425,286 2/1969 Ellis..74/568 3,344,685 10/1967 Grouzet ..74/569 1,525,052 2/ i 925 Spotz..74/568 2,777,513

l/l957 Cooper "74/568 Primary Examiner--William F. ODea AssistantExaminer-Wesley S. Ratliff, Jr. Attorney-Ralph G. Hohenfeldt and FredWiviott 5 7 ABSTRACT Optimum fuel-to-air ratio over the entire operatingrange of a boiler fuel burner is obtained by having a motor, which isdriven in response to boiler temperature or pressure changes, operate adamper and fuel valves simultaneously. A cam and follower reposition thefuel valves coordinately with a directly driven damper, Means areprovided to adjust the cam contour over its length so optimumfuel-to-air ratios prevail for all positions of the damper. The followeris positively engaged with the cam.

4 Claims, 4 Drawing Figures PATENTEU M1822 1912 3,685,364

SHEET 1 [IF 2 //V VE N TOPS,

I JOSEPH L. TURECEK DAVID T. FEULING GLENN D CRAIG I H By WwawPAIENTEDmczzmz 3.685 364 sum 2 or 2 if? i 5% 7;. 25 i@ E :T:

INVENTORS,

JOSEPH L.TUYRECEK DAVID T. FEULING GLENN D. CRAIG BY wi ww Attorney CAMFOR CONTROL OF COMBUSTION FUEL-TO- AIR RATIO BACKGROUND OF THE INVENTIONIn connection with boilers, furnaces and other heating devices it isnecessary to modulate the fuel combustion rate in accordance with thetemperature that is desired. In a gas or oil fired boiler, for example,a transducer or a sensor may produce a force or signal which correspondswith pressure or temperature of the water or steam, respectively. Thissignal may act through a control to actuate a damper motor which adjuststhe amount of air and, simultaneously, the amount of fuel required foroptimum combustion efficiency.

It has been common practice to adjustfuel flow by letting the dampermotor drive a variable contour cam whose follower actuates the fuelvalves. To provide a fuel flow which matches the air flow for obtainingefficient combustion at all discrete settings, flexibility must be builtinto the system because the flow characteristics of the fuel valves aresubstantially different than those of the air dampers. For instance, aspecific movement of the air damper will provide an air flow which isnot necessarily compatible with the fuel flow resulting from thecorresponding movement of the fuel valve. Thus, an adjustable contourcam is required with flexibility to rotate or otherwise actuate the fuelvalves more or less so that the fuel-to-air ratio can be properlyestablished for any combustion rate.

Fuel valve control cams whose contour or profile may be varied overincrements of the length of the cam surface have been used before.However, prior types have some disadvantages. If there was someresistance to return movement of the fuel control valve linkages therewas often insufficient force in the cam follower spring for the followerto be held in contact with the cam. The result was that fuel flow rateto the burner was not always held in proper proportion to the air flowfor optimum combustion efficiency.

SUMMARY OF THE INVENTION An object of the present invention is toovercome the aforementioned and other disadvantages by providing a camand follower assembly in which the cam contour or profile may beadjusted incrementally as desired and in which the follower is movablybut positively engaged with the cam surface.

Another object is to provide a reliable, relatively simple andinexpensive fuel valve control cam assembly.

Briefly stated, one embodiment of the invention involves mounting anarcuate and bidirectionally movable cam segment on a journaled shaft forjoint.rotation with a link that is driven from the damper motor. Thearcuate cam segment has a pair of nominally concentric spaced apartmetal cam strips which are engaged in their intermediate gap by aplurality of circumferentially spaced cam strip engaging members orheads. Each member is supported from the arcuate seg ment by anadjusting screw which may be turned to adjust the member and the segmentof the cam which it engages to a preselected distance from the center ofrotation. The cam strips may then have a generally uniformly curvedprofile but with minor undulations at incremental zones where correctingadjustments are made.

- The cam strips have exposed edge margins so that spaced rollers on acam follower may positively engage the top and bottom surfaces of thecam strips and thereby be compelled to follow the cam strip contour andproduce a positive lineardriving force on the follower.

How the foregoing and other more specific objects are achieved willappear from time to time in the ensuing description of an embodiment ofthe invention taken in conjunction with the drawing.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a dampercontrol motor and a fuel control valve which is operatively connected bythe new cam assembly;

FIG. 2 is a side elevation view of the isolated cam and followerassembly;

FIG. 3 is an elevation view taken from the right'side of the assemblyshown in the preceding figure; and

FIG. 4 isa fragmentary vertical sectional view of the cam adjustingscrew and affiliated parts.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 illustrates one type ofconventional boiler fuel valve assembly comprising a body 10, somepressure gauges l1 and 12, and a pair of manual flow control handles 13and 14. The rate at which fuel is metered through the valve depends, inthis example, on linear movements of a valve stem 15. Rotary valves arealso used for metering gas or liquid fuels in some installations. Onboilers that are adapted for switching from one type of fuel to another,both liquid and gas fuel valves may be present. The valves may be rotaryor linear types and they may each be controlled by one of the new camassemblies disclosed herein.

In the upper left of FIG. 1 the damper control motor 16 is illustrated.This motor responds to signals indicative of required changes incombustion conditions by rotation of its shaft 17. The shaft has pinnedon to it an arm 18 which has several adjusting holes and is pivotallyconnected to a turnbuckle link 19. The turnbuckle link is pivotallyconnected to an arm 20 which is fixed on a jack shaft 21. An air dampermay be driven directly by arms from jack shaft 21. The damper and armsare not shown.

The jack shaft is joumaled for rotation in a bearing 22 which is securedin a bearing bracket 23. Pinned on jack shaft 21 by means of a set screw24 or other suitable means is a cam base 25 which has an arcuatelongitudinally extending flange 26. A plurality of socketheaded screws27 extend radially through the flange 26. These screws 27 are threadedin flange 26 in this embodiment.

Each screw 27 carries a cam contour adjusting head member 28 at theradially remote end of the screw. For brevity, these members will becalled heads 28. The heads 28 have slots 29 on their opposite sides. Athin strip of metal 30, constituting a deformable-contour cam surface,is fitted into the corresponding slots 29 in a row on one side of theheads. There is another cam strip 31 similarly located in the row ofslots on the other side of heads 28. These parallel cam strips 30 and 31have a gap 32 between them so that the center portion of heads 28 canpass between them. The ends of cam I strips 30 and 31 are tied togetherby a strap 33 which is secured to the cam strips by means of screws 34and 35. The cam strips 30 and 31 are similarly joined at both ends tofix them in parallel spaced relationship.

Because cam strips 30 and 31 are positively engaged by slots 29 in heads28, it should be evident that increments of the contour or profile ofthe deformable cam strips can be changed or shaped with undulations byvariously adjusting the radial distance of the individual heads 28 fromthe cam base flange 26. This is accomplished by turning adjusting screws27 in or out with an Allen wrench. Thus, it is possible to establish thegeneral contour of the cam strips 30 and 31 with adjusting screws 27 andit is also possible to change the profile of a selected cam strip lengthincrement by ad justing a screw 27 in the head 28 that engages the camstrip where the profile of the increment is to be different thanadjacent increments.

FIG. 4 shows how the contour adjusting screws 27 and the adjusting heads28 are coupled. One may see that screw 27 has its diameter reduced inthe region 36 so it passes through head 28 with a little clearance. Thereduction in diameter results in formation of an annular shoulder 37which prohibits axial upward movement of head 28. The terminal end 38and screw 27 is countersunk and flared for retaining the head 28. Awasher 39 is interposed between flared portion 38 and head 28 to providea smooth bearing surface and to reduce friction when the screw is turnedin the head to advance or retract it. Note in FIG. 4 that cam strips 30and 31 extend laterally a considerable distance outside of slots 29 toprovide upper and lower cam follower bearing surfaces 40 and 41 whichare marked only on cam strip 30.

Referring again to FIG. 1, one may see that the cam follower whichdrives fuel valve stem comprises a yoke which is generally designated42. The yoke has a cross member 43 and a set screw 44 for fastening toit valve stem 15. The yoke also has a pair of spaced apart upstandingside members 45 each of which carries a pair of rollers 46 and 47. Therollers are on stub shafts 48 the ends of which are threaded into sidemembers 45. The peripheral surfaces of the adjacent roller pairs ofspaced apart a distance that is substantially equal to the thickness ofcam strips 30 and 31. Rollers 46 and 47, therefore, follow faithfullyall incremental undulations in the cam strip profiles. The fact that thecam strips are captured between the rollers results in follower 42 beingdriven forcibly in a vertical direction and the cam and follower cannotseparate regardless of any resistance that may be offered by the valvestem 15 and its associated mechanism.

As stated earlier, arms extend from jack shaft 21 for operating the.damper. The damper and arms are not shown since they are not part of thenovel subject matter and it is only necessary to recognize for presentpurposes that the damper is repositioned in response to changing boilerconditions. The fuel valve is readjusted correspondingly at the sametime. With the new cam assembly, the cam contour may be adjusted so thatoptimum fuel-to-air ratios are obtained for all settings of the damper.

The new positive drive cam assembly is subject to some structuralmodifications without departing from the principles of the invention.For instance, the structure shown in FIG. 4 may be made conversely. Thatis,

the unthreaded portion 36 of the adjusting screws 27 may pass through aclearance hole in flange 26 and may be captured therein for rotation,and the threaded portion may be threadingly engaged with head 28.Rotation of screw 27 will still actuate the head radially inwardly oroutwardly to change the cam strip profile.

The only limiting condition is that the cam follower must engage the camsurface by capturing it on both sides. The heads 28 could also becircularly slotted spools fastened to the screws 27 by turning andadvancing and retracting with the screws.

In its broadest sense the invention requires a cam surface supportingmember that is subject to rotational or translational movement relativeto a follower which is positively engaged with the cam surface. Themovement may be caused by any condition responsive force producingdevice. The cam surface is adapted for having increments of its lengthmodified in profile so that the follower will move a distance which isdisproportionate to the cam surface movement as may be predetermined atwill. In the illustrative embodiment the cam surface members are mountedon heads which have individual adjusting screws extending from andthreaded through anarcuate support. Various adjustable means other thanscrews could engage the heads and the heads or their equivalents couldbe replaced with other cam surface engaging means. Moreover, the camsurface could be mounted for translation in an angular plane in whichcase any incremental profile variations would still be transmitted tothe follower.

Although a preferred embodiment of the invention has been described indetail, it will be understood that such description is to be consideredillustrative rather than exclusive, for the invention may be variouslyembodied and is to be limited in scope only by interpretation of theclaims which follow.

We claim:

1. A positive drive cam and follower assembly comprising:

a. a rotatable element having an arcuate part displaced radially fromits axis of rotation,

b. a row of adjusting screw means extending radially from said arcuatepart and turnable therein,

c. cam member supporting head means relatively rotatably mounted on saidscrew means,

. a cam member, increments of which are deformable in a radialdirection, said cam member having radially opposed surfaces and beingengaged at spaced intervals by head means in a row, said head meanshaving laterally extending slot means receiving said cam member andpositively engaging each of said opposed cam surfaces, whereby selectiverotation of the adjusting screw means will positively deform incrementsof said cam member correspondingly radially toward or away from saidrotatable element, and

e. a cam follower means including spaced apart roller means in positivecontact engagement respectively with said opposite surfaces of the cammember so that the follower means are compelled to move in radialdirections corresponding with the profile of the cam member.

2. The invention set forth in claim 1 wherein:

a. said cam member comprises a pair of metal strips which are similarlycontoured and spaced apartin parallelism with each other,

b. the slot means of said head means snugly engaging and supporting eachof said strips at spaced intervals along their lengths.

3. The invention set forth in claim 2 wherein:

a. said metal strips comprising the'cam member extend laterallyoutwardly in opposite directions from the slots to define the saidopposed cam surfaces,

b. said follower means comprising yoke means on each side of which arepairs of roller means having parallel axes of rotation and which havetheir peripheries spaced part a distance that is substantially equal tothe thickness of the metal strips, whereby the profile of the cam memberstrips that is presented continuously between the rollers due to camrotation positively drives the cam follower means bidirectionally.

- 4. A cam assembly for closely coordinating the condition of the fueland air flow control means of a burner wherein a cam follower means isdriven in a positive manner bidirectionally to control the burner,comprismg:

a. a rotatable element having an axially projecting curved flange means,

b. a row of adjusting screw means radially threaded through the flangemeans and having unthreaded portions at their ends remote from theflange means,

c. a head means disposed on each unthreaded portion of the screw meansand means retaining the head means thereon but permitting rotation ofthe screw means therein for individually advancing or retracting saidhead means radially,

d. said head means each having opposed laterally extending slotsdefining parallel opposed rows of slots, I

e. a pair of thin deformable continuous metal cam strips each having acorresponding edge spaced from and disposed in parallel with the otherand with said edges being engaged in said respective rows of slots sothat a cam profile is defined by the other edges of the strips whichproject from the slots, the said other edges having opposed camsurfaces,

f. a cam follower on which are mounted opposed pairs of rollers whichhave parallel axes of rotation, the peripheries of the rollers in a pairbeing spaced apart a distance that is substantially equal to thethickness of the cam strip, said roller peripheries in a pair being incontact simultaneously with said opposed cam surfaces for positivelydriving said follower linearly in correspondence with the cam profileincrement that is presented between the rollers by rotation of the saidrotatable element.

1. A positive drive cam and follower assembly comprising: a. a rotatableelement having an arcuate part displaced radially from its axis ofrotation, b. a row of adjusting screw means extending radially from saidarcuate part and turnable therein, c. cam member supporting head meansrelatively rotatably mounted on said screw means, d. a cam member,increments of which are deformable in a radial direction, said cammember having radially opposed surfaces and being engaged at spacedintervals by head means in a row, said head means having laterallyextending slot means receiving said cam member and positively engagingeach of said opposed cam surfaces, whereby selective rotation of theadjusting screw means will positively deform increments of said cammember correspondingly radially toward or away from said rotatableelement, and e. a cam follower means including spaced apart roller meansin positive contact engagement respectively with said opposite surfacesof the cam member so that the follower means are compelled to move inradial directions corresponding with the profile of the cam member. 2.The invention set forth in claim 1 wherein: a. said cam member comprisesa pair of metal strips which are similarly contoured and spaced apart inparallelism with each other, b. the slot means of said head means snuglyengaging and supporting each of said strips at spaced intervals alongtheir lengths.
 3. The invention set forth in claim 2 wherein: a. saidmetal strips comprising the cam member extend laterally outwardly inopposite directions from the slots to define the said opposed camsurfaces, b. said follower means comprising yoke means on each side ofwhich are pairs of roller means having parallel axes of rotation andwhich have their peripheries spaced part a distance that issubstantially equal to the thickness of the metal strips, whereby theprofile of the cam member strips that is presented continuously betweenthe rollers due to cam rotation positively drives the cam follower meansbidirectionally.
 4. A cam assembly for closely coordinating thecondition of the fuel and air flow control means of a burner wherein acam follower means is driven in a positive manner bidirectionally tocontrol the burner, comprising: a. a rotatable element having an axiallyprojecting curved flange means, b. a row of adjusting screw meansradially threaded through the flange means and having unthreadedportions at their ends remote from the flange means, c. a head meansdisposed on each unthreaded portion of the screw means and meansretaining the head means thereon but permitting rotation of the screwmeans therein for individually advancing or retracting said head meansradially, d. said head means each having opposed laterally extendingslots defining parallel opposed rows of slots, e. a pair of thindeformable continuous metal cam strips each having a corresponding edgespaced from and disposed in parallel with the other and with said edgesbeing engaged in said respective rows of slots so that a cam profile isdefined by the other edges of the strips which project from the slots,the said other edges having opposed cam surfaces, f. a cam folloWer onwhich are mounted opposed pairs of rollers which have parallel axes ofrotation, the peripheries of the rollers in a pair being spaced apart adistance that is substantially equal to the thickness of the cam strip,said roller peripheries in a pair being in contact simultaneously withsaid opposed cam surfaces for positively driving said follower linearlyin correspondence with the cam profile increment that is presentedbetween the rollers by rotation of the said rotatable element.